Yucatan Sailfin Molly Breeding Guide

Breeding Poecilia velifera, the giant sailfin molly: sexing by the tall male sail and gonopodium, hard-water conditioning, 28-40 day gestation and care of 9-11 mm fry.

Overview

Poecilia velifera, the Yucatan or giant sailfin molly, is the largest sailfin molly, native to the Yucatan Peninsula of Mexico where it occurs in coastal lagoons, estuaries and salt marshes as well as freshwater. It tolerates a broad range of salinities but is most successful in freshwater, and is listed as Vulnerable by the IUCN. Most aquarium stock is captive-bred, and many fish sold as P. velifera are P. latipinna x P. velifera hybrids. It is a livebearer.

Sexing

Males are somewhat larger than females, reaching 7.2-9.25 cm total length versus 4.5-7.2 cm in females. Mature males develop a tall sail-like dorsal fin bearing 15 to 21 rays, taller than that of any other molly, and carry a gonopodium. Males are polymorphic in size and colour, with large ornamented, intermediate ornamented and cryptic intermediate classes.

Conditioning

The species occurs at 25-30 °C in the wild and prefers still or slow-moving water; as a sailfin molly it requires hard alkaline water and does poorly in soft, acidic conditions. It is primarily herbivorous, favouring filamentous algae and diatoms but also taking crustaceans and insects, so conditioning diets should be rich in vegetable matter.

Mating & Gestation

Fertilization is internal via the gonopodium. Gestation is approximately 28 to 40 days at 25-30 °C. In the wild breeding extends from late February to late July. Brood size varies with female size: about 47 fry at 6 cm total length, averaging around 77, ranging from as few as 10 to up to 120 young.

Birth & Fry Care

Newborns are about 9-11 mm total length regardless of mother size, and are large enough to take small live and prepared foods immediately. A spacious, well-planted setup suits this large species; a 110-litre aquarium may house only a pair or trio. As with other mollies, dense planting or separating the gravid female protects fry from predation.

Common Challenges

Adult males grow large and need substantial tank volume, and full sail development depends on good water quality and adequate vegetable matter. Soft or acidic water is harmful. Because much commercial stock is hybridized, fish intended for breeding true P. velifera should be sourced carefully.